1. Field of the Invention
The present invention relates to an image stabilization control technology that corrects or prevents image shake or image degradation occurring due to shaking such as hand shake.
2. Description of the Related Art
In recent years, all operations of a camera significant to image capture, such as the operation for determining the exposure and a focusing operation, may be performed automatically. Accordingly, even a user who is not accustomed to using a camera may nearly always succeed in taking high quality pictures. For example, there is a function for performing continuous focusing in auto-focus (AF) processing using image processing technology during moving image photographing or while an EVF image is continuously taken so as to cause a display device associated with an image capturing apparatus to function as an electronic view finder (EVF). This is known as a “continuous AF function”. In order to prevent image shake due to hand shake or the like, a camera including an image stabilization control apparatus consisting of a shake correction unit, a driving unit, a shake detection unit, and the like eliminates almost all of the factors that induce a shooting mistake by a photographer.
Here, an image stabilization control apparatus will be briefly described. The hand shake that may occur with a camera during image capture is a shake with a frequency of generally 1 to 10 Hz. To take a photograph without any image shake even when such hand shake is applied to a camera when the shutter is released, it is necessary to detect the angular rotational shake applied to the camera due to hand shake and displace a lens for correcting image shake (hereinafter simply referred to as a “correction lens”) according to the detected value.
Meanwhile, when an image is taken at a short distance (under a capture condition in which a high imaging magnification is used), image degradation caused by translational shake, which may not be detected by an angular velocity sensor alone and is applied to the horizontal direction or the vertical direction lying in a plane perpendicular to the optical axis of the camera, may not be ignored. For example, when a subject image is taken at such a close subject distance of about 20 cm in the case of macro photography, it becomes necessary to actively detect and correct the translational shake. Under capture conditions in which the focal length of an imaging optical system is very large (e.g., 400 mm) even when a subject distance of 1 meter is ensured, it also becomes necessary to detect and correct the translational shake.
Japanese Patent Laid-Open No. 7-225405 discloses a technology in which an accelerometer configured to detect acceleration is provided to determine translational shake by taking the second integral of the detected acceleration and drive a shake correction unit according to the detected translational shake value and an output from an angular velocity meter, which is provided separately. Japanese Patent Laid-Open No. 2010-25962 discloses a technology in which translational shake is determined by taking angular rotational shake when the rotation center is located far from the camera.
However, in the correction of translational shake using the image stabilization control, the shake amount to be corrected on an imaging surface due to translational shake becomes greatly different due to the difference between photographing a subject at a short distance and photographing a subject at a long distance (i.e., difference in imaging magnification). In this case, a shake correction amount for correcting image shake occurring due to translational shake is calculated using the imaging magnification of an image-taking lens, which has been obtained by positional information about a zoom lens and a focus lens.
Even if the translational shake amount of the camera is the same, the imaging magnification may change from time to time during an AF operation. Thus, a translational shake correction amount to be corrected on the imaging surface also changes depending on the imaging magnification. If the image stabilization control is performed in accordance with information about the imaging magnification obtained from the zooming or focusing state while the camera is searching for a peak of the AF evaluation value by a contrast AF operation, image stabilization performance may be degraded.
More specifically, when a focus lens is driven in a direction of increasing an imaging magnification (the movement in the close-up side), a translational shake correction amount becomes excessive, resulting in an adverse effect on shake correction. Furthermore, a correction lens immediately reaches the control terminal thereof due to excessive control, resulting in a degradation of the image stabilization control performance.
The present invention provides an apparatus that performs the image shake correction of translational shake with high accuracy while reducing the degradation of the image stabilization control performance in association with a sudden change in image magnification during imaging, and a method for controlling the same.